Test Your Knowledge

Sunscreen does not provide complete protection from the sun’s harmful ultraviolet (UV) radiation. When used properly, however, sunscreen can greatly reduce the effects of UV rays.

Sunscreen should be applied to dry skin about 20 to 30 minutes before heading outdoors. This gives the skin time to absorb the sunscreen and ensures that the sunscreen is working before skin is exposed to the sun. Depending on which form of sunscreen is being used (e.g., lotion, gel), a person may benefit from shaking the sunscreen container well before using its contents. This helps mix particles that may be clumped together in the container.  

Enough sunscreen should be used to completely cover all areas of exposed skin, including the nose, ears, neck, hands and feet. Sunscreen should also be applied to any areas of the scalp that are exposed. When using sunscreen in the form of a lotion, gel, ointment or cream, one ounce (or enough to fill a shot glass) is the recommended amount for an average-sized adult. A sunscreen–containing lip balm with a sun protection factor (SPF) of 15 or higher should also be used to cover the lips.

It is safe to apply makeup over sunscreen. Sunscreen-containing cosmetics are also available. People should avoid getting sunscreen into their eyes. Sunscreen that comes in contact with the eye often causes a temporary stinging sensation.

Sunscreen can be washed off, rubbed off or sweat off. As a result, it requires frequent reapplication. People should follow the manufacturer’s directions regarding reapplication. In general, sunscreen should be reapplied at least every two hours, regardless of the SPF. Even waterproof and water-resistant sunscreens require reapplication every two hours. It should also be reapplied immediately after getting out of water.  

Sunscreen-containing lip balm should also be reapplied at least once an hour, as well as before and after swimming, after eating and drinking and during any other activity that would remove it from the lips.

Over time, the ingredients contained in sunscreen begin to degrade. In order to ensure that sunscreen will be effective, people should keep track of when they purchase a particular product. Unless otherwise indicated by an expiration date, the U.S. Food and Drug Administration (FDA) requires that sunscreens remain at their original strength for at least three years.

Some sunscreens also contain insect repellants (e.g., DEET). The combination of these ingredients can decrease the effectiveness of the sunscreen and increase the absorption of DEET. Therefore, patients are encouraged to use separate sunscreen and insect repellant products. People who choose to use these combination products may benefit from using a product with a higher SPF and reapplying the sunscreen more often.

In rare cases, people may experience skin rash or irritation after applying sunscreen. This can result from having sensitive skin or an allergy to a fragrance, preservative or other component in the sunscreen. People should contact their physician when severe forms of these symptoms develop or fail to fade away. Patients may be able to prevent future reactions by using a different brand of sunscreen.